Pathways leading to formation of surface membrane-bound IgGl ("Ig-mem") or to secretion of IgGl in a cloned, murine myeloma cell line (MOPC-21) are being analyzed in vitro. Ig-mem and secreted IgGl appear to be separate end-products derived from a common precursor. Certain inhibitors of protein synthesis reduce the rate of Ig-mem acquisition without effecting secreting of pre-existing intracellular IgGl. Paradoxically, puromycin inhibits protein synthesis without effecting the rates of Ig-mem acquisition or secretion. This phenomenon is being explored further. A parallel project has been developed in which the role of memory cells possessing surface IgGl in a normal, secondary humoral immune response is being studied. We have identified memory cells possessing surface IgGl and are examining the effects of specific elimination of such cells on an adoptive secondary immune response in Balb/c mice. BIBLIOGRAPHIC REFERENCE: Guyer, Ruth L., Koshland, Marian E. and Knopf, Paul M., Immunoglobulin binding by mouse intestinal epithelial cell receptors, J. Immunol. 117:587-593, 1976.